THANK YOU - BA Refund Helper.
She / he responded to my original question within 48 hours, we had three email exchanges and though they were unable to resolve the problem, she/he did confirm the date and amount which was refunded against the locator code. (which was over a week after the call centre had stated!) We were then able to lean more heavily on RBC Visa, and within 24 hours, the "lost" refund somewhere in the wormhole between BA and VISA was located and credited. It wasn't quite the amount we were expecting as there was also a refund on the First class return moved to Biz after european flights were cancelled leaving a really poor connection at Heathrow but we got almost all of it. (one day I'll do First again (says him dreaming!))
If you are struggling to get through or make progress on a refund, this resource is highly recommended. Thorough, polite and moved us forward in searching for the two grand!
Regardless of whether this is an official service or not, BA Refund Helper should be formally recognised for her / his personal commitment to delivering excellent customer service. (and get a whole load of FTalkers off the phones and "happy" - a relative term for most on this forum!)